1. Field of the Invention
The present invention relates to a character recognition processing, in particular, to a character recognition processing capable of rapidly recognizing degraded character images.
2. Description of Related Art
As one of the issues in Optical Character Recognition (OCR) in which written or printed characters are optically read and recognized, sometimes it is necessary to recognize degraded character images accurately. In character recognition processing, if a size of a character image of a recognition image is sufficiently large or in an ideal state without blur or half-dry stroke, damage, noise and the like, the recognition precision is high. However, if the size of the character image is small or in the presence of blur or half-dry stroke, damage and noise, the character recognition precision will decrease. For example, if the size of the character image is small, blur may occur if the character size is enlarged through standardization processing, and thus the precision of the character recognition using a dictionary made according to ideal character images will decrease. In a situation where the character image of such a recognition object deviates from the ideal state, the character image may be degraded.
For example, as an application of OCR, a number plate recognition system is known, which uses a camera to shoot number plates hung on vehicles driving on the road, and recognizes described characters. In the past, the mainstream approach was arranging a camera above the road for each lane; however, in recent years, in consideration of limitations of device conditions or costs, a practice of fixedly arranging a camera on a lamp-post erected on a road side emerges. When the manner of arranging the camera on a road side is used on a multi-lane road, according to different distances from the lanes to the camera, a size of a number plate on a lane close to the camera is different from a size of a number plate on a lane away from the camera. A character image in a number plate of a distant lane becomes small, and through standardization processing, the character image may be degraded.
As a recognition method for degraded character images, Patent Document 1 may be listed. Patent Document 1 discloses: pre-making various dictionaries of degradation levels, and based on similarity between a character image of a recognition object and a test sample with a same degradation level, determining a degradation level of a dictionary to be used.